1. Field of the Invention
The present invention relates to a determination method in a CDMA mobile communication system that uses radio repeaters for determining whether a mobile station is within the service area of a repeater or within the service area of a radio base station.
2. Description of the Related Art
In a mobile communication system that uses the CDMA method, a plurality of methods that use the difference in propagation delay between a radio base station and a mobile station have been adopted as methods for detecting the position information of a mobile station (for example, RTD: Relative Time Difference, OTDOA: Observed Time Difference of Arrival). One method among these methods is disclosed in Japanese Patent Laid-Open Publication No. 2003-189351. In this method, the propagation delay differences between a mobile station and a plurality of (three or more) radio base stations are measured and the spatial position of the mobile station then calculated based on this information.
When calculating the transmission power of a physical channel that is used in radio communication between a mobile station and a radio base station, the propagation loss value of the radio propagation path between the radio base station and the mobile station is used. More specifically, the determination of the value of initial transmission power of the Dedicated Physical CHannels (DPCH) and the determination of the value of the transmission power of the Forward Access CHannel (FACH) in a CDMA mobile communication system are carried out by the following procedures:
(1) The radio base station reports the transmission power value of the Primary Common Pilot CHannel (PCPICH) by means of report information.
(2) The mobile station measures the reception power value of the pilot channel (PCPICH) in its own area.
(3) The mobile station reports the reception power value of the PCPICH to the radio base station by means of a Random Access CHannel (RACH).
(4) The radio base station estimates the propagation loss between the radio base station and the mobile station from the difference between the value of the PCPICH transmission power ((1) above) and the value of the reception power that was reported from the mobile station ((2) above).
(5) The radio base station calculates the initial transmission power value from the calculated propagation loss.
This accurate measurement of the propagation loss and the propagation delay on the propagation path between the radio base station and mobile station is necessary for the various types of control of the mobile communication system such as the detection of position information of the mobile station or the control of transmission power.
However, when this type of method is applied to a CDMA mobile communication system that uses radio repeaters, the problem arises that propagation delay and propagation loss cannot be accurately measured. Such a mobile communication system that uses repeaters is described in, for example, Japanese Patent Laid-Open Publication No. 2001-274745, in which repeaters are arranged between a radio base station and a mobile station whereby new service areas are provided that are different from the service area of the radio base station. In a mobile communication system in which repeaters are arranged within the service area that is provided by a radio base station, signals are transmitted and received by way of a radio base station, a repeater and then a mobile station when a mobile station is within the service area of a repeater.
The control delay of the radio signals in the repeater that consequently occurs in the propagation path that passes by way of the repeater therefore causes the problem of preventing the accurate estimation of the propagation delay between the radio base station and the mobile station. In the above-described service of detecting the position information of the mobile station, the inability to accurately estimate the propagation delay in turn prevents the accurate estimation of the position information of the mobile station.
In addition, the method of calculating the initial transmission power of the above-described prior art is based on the assumption that the propagation loss in the downlink direction (the direction from the radio base station to the mobile station) and the propagation loss in the uplink direction (the direction from the mobile station to the radio base station) are equivalent. However, in a radio link in which a repeater is interposed, the gain in the repeater cannot be assumed to be equal in the downlink direction and the uplink direction, and this imbalance may in turn prevent the adequate determination of the transmission power value.
A CDMA mobile communication system of the prior art in which repeaters are arranged between radio base stations and mobile stations therefore has the following problems:
(1) When attempting to detect position information of a mobile station by measuring the propagation delay between a radio base station and the mobile station, the control delay of radio signals that occurs in a repeater prevents the accurate estimation of the propagation delay between the radio base station and the mobile station in a propagation path that passes by way of a repeater and thus prevents the proper detection of position information.
(2) When attempting to measure the propagation loss between a radio base station and a mobile station, the possibility for inequality of the gain in a repeater in the downlink and uplink directions in a propagation path that passes by way of a repeater prevents the accurate measurement of the propagation loss, and prevents the realization of adequate transmission power control.
However, the control delay, which is the amount of delay in a repeater, is a value that is known in advance; and reporting the radio gain, which is the gain by which radio signals are amplified in a repeater, from the repeater to the radio base station allows a radio base station to ascertain the degree of amplification in the repeater for uplink and downlink lines. Thus, if it can be determined whether a mobile station is currently within the service area of a radio base station or within the service area of a repeater, a radio base station should be able to more accurately estimate the propagation loss and propagation delay between the radio base station and the mobile station. However, a method has yet to be proposed for determining in a radio base station whether a mobile station is currently within the service area of a radio base station or within the service area of a repeater.